1. Field of the Invention
The present invention relates to a scattered radiation imaging apparatus which is capable of obtaining a good image of low Z materials, such as plastic explosives and narcotics, that had been undetectable in previous technology, for the purpose of detecting entrance of articles which are considered dangerous (such as plastic explosives) or are regulated by law (such as narcotics) in the security field, especially at airport and other regions.
2. Description of the Background Art
One conventional technique for detecting Low Z materials which is employed in the prior art is exemplified by Annis et al U.S. Pat. No. 4,799,247.
The apparatus described is shown in FIG. 1. In this apparatus, an X-ray source 1 provides a generally conical beam of X-rays which is directed at radiation opaque plate 2 with a slit 3. The slit 3 allows a sheet-like X-ray beam to pass to a rotating disk 4 formed with a slit 5. As the rotating disk 4 rotates, the rotating disk 4 intercepts the sheet beam. And the slit 5 allows a pencil beam 6 to pass. The pencil beam 6 scans an object 7 to be inspected, and a conveyor 9 carries the object 7 in the direction of arrow 8 across a line of pencil beam 6.
A back scatter detector 10 responds to back scatter X-rays (particularly by Compton scattering) as they reflect back from the object 7 and outputs back scattered signals corresponding to the back scattered X-rays.
The back scattered signals are provided to the scatter electronics 11 where they may be summed and used to develop a video signal for driving display 12 which is a scatter imaging device.
The transmitted detector 13 responds to X-radiation transmitted through the object 7, and outputs transmitted signals to a transmitted electronics 14 corresponding to the transmitted X-ray.
In the same way, a display 15 shows a transmitted X-ray image based on the transmitted signals.
Since high Z materials readily absorb more X-rays than low Z materials, the transmitted image can readily be used to identify the shape of any high Z material by the particular shape of the shadow the high Z material produces.
The scatter image can similarly be used to identify the shape of any low Z material by the particular shape of the shadow the low Z material produces.
This apparatus of FIG. 1 is effective in carrying out the inspection of the object, but is also known to have the following problems.
In this apparatus, the flying spot scanner and detectors are horizontally arranged, and the pencil beam is irradiated in the horizontal direction.
Thus, the shape of the apparatus is horizontal. Therefore the apparatus occupies a large floor space.